Mistake by DWP workers cuts electricity across the L.A. area. Public officials express doubts about the city system's integrity.

A mistake on a single bundle of wires Monday cascaded into a major blackout in and around Los Angeles, inconveniencing millions of people and renewing questions about the vulnerability of the region's power system.

Coming one day after a purported Al Qaeda threat of attack on the city, the midday outage pricked nerves and caused isolated incidents of panic. Plumes of flame and smoke heightened the drama as refineries, temporarily shut by the outage, flared off excess gases.

But backup generators, many newly installed since California's 2001 energy crisis, kept many companies and most emergency services operating without major disruption, and there were no reports of deaths or serious injuries caused by the blackout.

The Los Angeles Department of Water and Power, the city-owned utility, said the outage occurred when workers cut through wires while installing a monitoring system at an electrical transmitting station in Toluca Lake.

The mistake rippled through the electrical grid, threatening to overload another transmission station and two electrical generating plants: the Scattergood generating station south of Los Angeles International Airport and the Haynes generating station near Long Beach.

The DWP shut down the generating facilities to avoid damage, sharply reducing the amount of power available to the city. That caused blackouts in neighborhoods across the city, with heavy concentrations in parts of the San Fernando Valley, South Los Angeles and the downtown area. All of Burbank's 52,000 customers and half of Glendale's 80,000 also lost power. Both cities' electrical systems are linked to the DWP.

"This strikes me as something under the category of unbelievably bad luck, where you cut one line and have that kind of cascading effect," said Bob Finkelstein, executive director of the Utility Reform Network in San Francisco, a consumer advocacy group.

"One DWP worker is going to feel really, really bad for a long time."

The automated system workers were installing was meant to detect surges or drops in voltage, said Ed Miller, the DWP's director of power systems, operations and maintenance.

"They cut a bundle of wires," Miller said. "The supposition is that by cutting them together, they created a short that triggered the circuit breakers." Miller said cutting wires one by one might have avoided an electrical short.

Ironically, the system the work crew was trying to install would have identified the power problem much more quickly, Miller said. It would be able to "decipher just what had happened." As it happened, DWP engineers needed an hour to determine where in the system the outage began.

An official with the union that represents DWP workers charged that, regardless of whether lines were cut, the real cause of the outage was the DWP's decision to test the new relay system in the middle of the day, rather than at night when power loads would have been lower -- but costs would have been higher because of overtime.

"They are too cheap to pay overtime, so they are testing on a full load at 1 in the afternoon," said Brian D'Arcy, business manager for the International Brotherhood of Electrical Workers, Local 18.

"You clearly don't test the relay at one in the afternoon. If you are cheap and stupid, this is what happens."

The DWP said such work is routinely conducted during the day.

DWP officials insisted the system had worked as it is supposed to -- shutting down and causing a temporary inconvenience to avoid widespread permanent damage. Miller compared the shutdown to the way a circuit breaker turns off power to a house to prevent overheated lines from causing a deadly fire.

At the same time, however, Miller said he planned to investigate whether the ability of a single incident to black out half the power supply indicated a need for major changes in the way the city's electrical system is configured. "If I decide I need a differently configured system, that could take a couple of years," he said.

"I'm very proud of my people. There was no system damage, and nobody was hurt," said Miller.

"The system is not fragile," he added. "We have a very strong system."

Others were less sanguine.

"As an engineer, it's unnerving that one individual act can cut power to hundreds of thousands of customers," said Los Angeles City Councilman Tony Cardenas, chairman of a panel overseeing the DWP.

Cardenas, who was stuck in traffic on Van Nuys Boulevard when traffic signals went out, said he would demand to know whether the outage betrayed a broader vulnerability for the city's electrical system.

"I've been told over and over that this kind of vulnerability doesn't exist," Cardenas said.

Mary Nichols, who heads UCLA's Institute of the Environment and was appointed last month as a DWP commissioner, said she, too, had "questions and concerns" about "why the system isn't more resilient and why there isn't more redundancy built into it."